Field of the Invention
The present invention relates to a silicon carbide substrate, a semiconductor device, and methods for manufacturing them. More particularly, the present invention relates to a silicon carbide substrate capable of improving yield of semiconductor device characteristics, a semiconductor device using the substrate, and methods for manufacturing them.
Description of the Background Art
In recent years, in order to achieve higher breakdown voltage and lower loss of a semiconductor device, use thereof in a high temperature environment, and the like, silicon carbide has increasingly been adopted as a material for forming a semiconductor device. Since silicon carbide is excellent in heat conductivity when compared with a semiconductor made of a nitride such as gallium nitride, it is excellent as a substrate for a semiconductor device for high-power application at high voltage and large current.
In order to form a high-quality epitaxial layer on a substrate, the substrate may be subjected to surface treatment before formation of the epitaxial layer. For example, Japanese Patent Laying-Open No. 2010-163307 describes a nitride substrate having a surface layer containing 3 atomic percent (at %) to 25 at % of carbon and 5×1010 atoms/cm2 to 200×1010 atoms/cm2 of a p type metal element. Thereby, a nitride substrate having a stabilized surface is obtained.
However, the state of a surface differs depending on the substrate material, resulting in differences in surface oxidation and easiness of adsorption or adherence of an impurity to the surface. Therefore, even if the method described in Japanese Patent Laying-Open No. 2010-163307 is applied to a silicon carbide substrate, it is difficult to obtain a silicon carbide substrate having a stabilized surface.